The present disclosure relates to differential transformer type magnetic sensors and image forming apparatuses.
Image forming apparatuses using toner as developer exploit a magnetic sensor to detect the residual amount or density of the toner. Various types of magnetic sensors are proposed. A magnetic sensor of differential transformer type as one of the types has a configuration in which a drive coil, a detection coil, and a reference coil are arranged on the same core.
The use of planer coils as the coils can reduce the size of the differential transformer type magnetic sensor. As one example of the differential transformer type magnetic sensor using the planer coils, there has been proposed a sensor in which a first coil (drive coil), a second coil (reference coil), a third coil (detection coil), and a fourth coil (drive coil) are arranged in a first layer, a second layer, a third layer, and a fourth layer, respectively, and insulating substrates are disposed between the respective layers.